Key Technological Study Of Earth Pressure Balance Shield Construction In A Tunnel Section Of The South To North Water Diversion Project Of Beijing

With the rapid development of urban tunnel project, EPB shield machine in construction speed, low labor intensity, less impact on the environment, construction and economic advantages have been widely used as the preferred soft ground tunnel construction, and technical and economic good of the good results achieved.But in the EPB shield construction process there are still some problems. Mainly include: the relationship between the shield machine forward speed;thrust, cabin earth pressure, cutter speed, excavated between the amount and speed of the screw conveyor; cutterhead unearthed obstruction and poor; how to make the value of Soil Pressure palm sub-surface to maintain a balance; variation of the construction process of the formation of displacement.In this paper, the South East Canal Beijing shield construction for practical engineering background, body excavated during the construction of improved soil, Soil Pressure variation of displacement values and formation were studied. Content specific study include:①The construction of improved soil. Designed a series of laboratory tests of soil improvement, respectively, fine sand and silty clay soil improvement(including additives performance test and improve indoor soil test), fine sand to get the best foam injection ratio is 8%, silty clay optimal ratio of 30% foam injection, and then based on the volume of mixed strata of fine sand and silty clay in different parameters to determine the best foam injection ratio was 22%.②Theoretical Calculations Soil Pressure. Apply different methods of calculation to obtain the theoretical excavation face shield pressure ranging 100-150 KPa.③ Ground displacement monitoring site. Measurements include:surface displacement, vertical displacement of soil, soil horizontal displacement and recording real-time operating parameters of shield machine. The results show that changes in the settlement formation is divided into three phases, upheave stage, rapid subsidence stage, slow subsidence stage; the variation of horizontal displacement is also divided into three stages, the change to the shield forward direction, the shield forward opposite direction changes and changes to the shield forward direction; shield total thrust, Soil Pressure and cutter torque are positive correlation and shield total thrust has a significant impact on the formation displacement。④Numerical simulation of ground displacement changes. In this paper, the actual monitoring software FLAC3 D Shield segment changes during construction to simulate ground movement. Variation of the simulated soil displacement and the actual displacement variation similar.The paper concludes with a guiding significance for the actual project, also can provide a reference for the construction of soft soil layer shield the country.